<!-- Any copyright is dedicated to the Public Domain.
     http://creativecommons.org/publicdomain/zero/1.0/ -->
<!doctype html>

<html>
  <head>
    <meta charset="utf-8"/>
    <title>WebGL editor test page</title>
  </head>

  <body>
    <canvas id="canvas" width="1024" height="1024"></canvas>

    <script type="text/javascript;version=1.8">
      "use strict";

      let canvas, gl;
      let customFramebuffer;
      let customRenderbuffer;
      let customTexture;

      window.onload = function() {
        canvas = document.querySelector("canvas");
        gl = canvas.getContext("webgl", { preserveDrawingBuffer: true });
        gl.clearColor(1.0, 0.0, 0.0, 1.0);
        gl.clear(gl.COLOR_BUFFER_BIT);

        customFramebuffer = gl.createFramebuffer();
        gl.bindFramebuffer(gl.FRAMEBUFFER, customFramebuffer);

        customRenderbuffer = gl.createRenderbuffer();
        gl.bindRenderbuffer(gl.RENDERBUFFER, customRenderbuffer);
        gl.renderbufferStorage(gl.RENDERBUFFER, gl.DEPTH_COMPONENT16, 1024, 1024);

        customTexture = gl.createTexture();
        gl.bindTexture(gl.TEXTURE_2D, customTexture);
        gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.NEAREST);
        gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.NEAREST);
        gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE);
        gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE);
        gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, 1024, 1024, 0, gl.RGBA, gl.UNSIGNED_BYTE, null);

        gl.framebufferTexture2D(gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0, gl.TEXTURE_2D, customTexture, 0);
        gl.framebufferRenderbuffer(gl.FRAMEBUFFER, gl.DEPTH_ATTACHMENT, gl.RENDERBUFFER, customRenderbuffer);

        gl.viewport(128, 256, 384, 512);
        gl.clearColor(0.0, 1.0, 0.0, 1.0);
        gl.clear(gl.COLOR_BUFFER_BIT);

        drawScene();
      }

      function drawScene() {
        gl.clearColor(0.0, 0.0, 1.0, 1.0);
        gl.clear(gl.COLOR_BUFFER_BIT);
        window.requestAnimationFrame(drawScene);
      }
    </script>
  </body>

</html>
